Ventilation controller

ABSTRACT

A ventilation system for a building in some cases includes a main HVAC blower for moving temperature-conditioned air through the building plus a smaller ventilation blower for providing fresh air. A controller regulates the ventilation blower&#39;s speed to provide a target ventilation flow rate regardless of changes in the pressure differential between the indoor and outdoor air. To ensure that the target rate is appropriate for a particular building, the target flow rate is determined based on a ventilation setting that reflects a specified number of bedrooms and a specified amount of floor space of the building.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of the prior filed and co-pending U.S.patent application Ser. No. 11/006,383 filed Dec. 7, 2004 by Robert W.Helt, et al., entitled “Ventilation Controller,” the disclosure of whichis incorporated by reference in its entirety.

FIELD OF THE INVENTION

The subject invention generally pertains to the ventilation of buildingsand more specifically to a ventilation system that delivers a generallyconstant airflow rate regardless of changes in the pressure differentialbetween the indoor and outdoor air.

DESCRIPTION OF RELATED ART

Heating ventilating and air conditioning systems, or HVAC systems, ofteninclude a blower and a heat exchanger for providing air that is heated,cooled, dehumidified, or conditioned in some way to meet the needs of abuilding and its occupants. Supply air ductwork can be used forconveying the conditioned air to various rooms of the building. Afterthe conditioned air (supply air) enters and circulates through therooms, the blower draws the used air (return air) back out of the roomsvia a network of return air ducts. The blower then forces the air backacross the heat exchanger for reconditioning.

In some cases, a tightly sealed home or building may create a staleindoor atmosphere due to an inadequate exchange of indoor and outdoorair caused by a lack of forced or natural ventilation. To maintain thefreshness or quality of the indoor air, an HVAC system may includeadditional ductwork and inlet dampers that permit a limited amount ofoutdoor air into the building. Under steady state conditions, theincoming fresh air displaces an equal amount of more stale indoor air.The displaced indoor air can escape the building by natural leakagethrough windows, doors, or other incidental cracks or openings in thebuilding.

Although sophisticated ventilation systems can be custom designed andconfigured for specific commercial and industrial buildings, such anapproach may be impractical for homes or smaller residential buildingsthat may be no more than three stories above ground. Even afterdetermining the ventilation airflow requirements of a particular home,it may be difficult to properly set up or adjust a conventionalventilation system to meet those requirements. Airflow measuringinstruments and trained service technicians may be needed to ensure thatthe system is properly set up for providing adequate ventilation. Someattempts, however, have been made to simplify the job of adjusting orsetting up a ventilation system for residential buildings.

Honeywell, for instance, provides a Y8150A Fresh Air Ventilation Systemthat allows a user to dial in a home's square footage and the number ofbedrooms. The system then calculates the required ventilation rate basedon ASHRAE Standard 62.2. To achieve the required ventilation rate,however, the system is first calibrated for the particular building inwhich the system is being installed. The calibration process determinesthe flow rate when the system's damper is wide open. By knowing thewide-open flow rate, the Honeywell system can cycle the damper open andclosed to provide, on average, the required ventilation rate. Such asystem, however, has a few drawbacks.

First, the Honeywell system relies on the building's main HVAC blowerfor drawing ventilation air into the building. Since such a blower isnormally much larger than that which would be needed for ventilationalone, energy is wasted during periods when only ventilation is needed.

Second, while calibrating the system, the main HVAC blower may beoperating at high or low volume depending on various factors such aswhether the HVAC is operating in a cooling or heating mode at the timeof calibration. Later, during normal operation, the blower's volume maychange from what it was during calibration, thus the actual ventilationrate may be off significantly.

Third, it does not appear that the Honeywell system accounts for changesin the static pressure differential between the indoor and outdoor air.Thus, the actual ventilation flow rate may be affected by opening andclosing windows and doors, operating bathroom exhaust fans, operatingkitchen exhaust fans, etc.

Consequently, a need exists for a standalone ventilation system that iseasily configured for various buildings.

SUMMARY OF THE INVENTION

A primary object of the invention is to provide a ventilation blowerthat is easily configured by inputting a setting that reflects abuilding's floor square footage and the number of bedrooms.

Another object of some embodiments is to provide a ventilation blowerthat is not only configured by inputting a setting that reflects abuilding's floor square footage and the number of bedrooms, but alsoregulates its airflow delivery, wherein the airflow delivery isdetermined based on the blower's speed and electrical current draw.

Another object of some embodiments is to provide a ventilation blowerthat is not only configured by inputting a setting that reflects abuilding's floor square footage and the number of bedrooms, but alsoregulates its airflow delivery by cycling the blower on and off at aduty cycle that provides a target average ventilation flow rate.

Another object of some embodiments is use a blower controller thatincludes a touchpad, computer, PDA, Internet communication, electricalswitch, dial, or infrared transmitter for manually inputting the settingthat reflects a building's floor square footage and the number ofbedrooms.

Another object of some embodiments is to provide a building with astandalone ventilation blower that is significantly smaller than thebuilding's main HVAC blower so that the main blower can be periodicallyturned off upon meeting a temperature conditioning demand while thesmaller blower can continue running at significantly less powerconsumption than what the main blower can consume.

Another object of some embodiments is to provide a ventilation blowerwith a controller that operates independently of a thermostat thatcontrols the operation of a main blower.

Another object of some embodiments is to provide a ventilation blowerwith a controller that is electrically coupled to a thermostat thatcontrols the operation of a main blower.

Another object of some embodiments is to provide a ventilation blowerwith a controller that shares the same enclosure as a thermostat thatcontrols the operation of a main blower.

Another object of some embodiments is have a ventilation blower move airbetween an outdoor area and a return air duct associated with abuilding's primary HVAC blower.

Another object of some embodiments is have a ventilation blower move airbetween an outdoor area and a supply air duct associated with abuilding's primary HVAC blower.

Another object of some embodiments is to provide a ventilation blowerthat is not only configured by inputting a setting that reflects abuilding's floor square footage and the number of bedrooms, but also aventilation blower that discharges air into the building.

Another object of some embodiments is to provide a ventilation blowerthat is not only configured by inputting a setting that reflects abuilding's floor square footage and the number of bedrooms, but also aventilation blower that discharges air out of the building.

Another object of some embodiments is to provide a ventilation blowerthat can be operated in a first mode for providing a required volume ofventilation air, and the blower can be operated in an economizer modewhere the ventilation flow rate is increased to provide “free cooling”when the outdoor conditions are right.

Another object of some embodiments is to provide a ventilation blowerthat delivers a generally constant airflow rate regardless of changes inthe pressure differential between the indoor and outdoor air.

Another object of some embodiments is to provide a ventilation blowerthat delivers a generally constant target airflow rate or equivalentaverage target airflow rate without having to first calibrate or measurethe actual flow rate when the system is first installed.

Another object of some embodiments is to provide a ventilation blowerthat delivers a generally constant target airflow rate regardless ofchanges in the ductwork leading to or from the blower.

Another object of some embodiments is to retrofit an existing bathroomor kitchen exhaust fan with a speed controller that provides a generallyconstant target airflow rate regardless of changes in the pressuredifferential between the indoor and outdoor air.

Another object of some embodiments is to provide a bathroom or kitchenexhaust fan with a dual-mode speed controller that in one mode providesventilation with a generally constant target airflow rate regardless ofchanges in the pressure differential between the indoor and outdoor air,and in the other mode provides a generally full volume airflow rate forexhausting smoke-contaminated or otherwise particularly low-quality air.

Another object of some embodiments is to provide a ventilation systemthat switches between a normal ventilation mode and a full-volumeexhaust mode in response to an occupancy sensor such as a light sensor,motion sensor, light switch, etc.

One or more of these and/or other objects of the invention are providedby a ventilation system that includes a primary HVAC blower and asmaller ventilation blower, wherein the ventilation blower is configuredby inputting a setting that reflects a building's floor space and thenumber of its bedrooms, and/or the ventilation blower provides agenerally constant ventilation flow rate substantially independent ofvariations in the differential pressure between the indoor and outdoorair.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a building with a primary HVAC systemand a separate ventilation system, wherein the ventilation systemincludes a blower discharging air into the building.

FIG. 2 is a schematic view similar to FIG. 1 but showing the ventilationblower exhausting air outside.

FIG. 3 is a schematic view similar to FIG. 1 but showing the ventilationblower discharging air into a supply air duct of the primary HVACsystem.

FIG. 4 is a schematic view similar to FIG. 3 but showing the ventilationblower discharging air into a return air duct of the primary HVACsystem.

FIG. 5 is a schematic view showing the ventilation system being furtherused as a bathroom exhaust fan.

FIG. 6 is a chart showing ventilation requirements for buildings ofvarious floor space and number of bedrooms.

FIG. 7 shows one example of a manual input for a controller.

FIG. 8 shows another example of a manual input for a controller, whereinthe manual input is used with reference to a chart.

FIG. 9 shows yet another example of a manual input for a controller.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 schematically illustrates a building 10 that includes a main HVACblower 12 for moving temperature-conditioned air 14 through the buildingand a smaller ventilation blower 16 for providing the building withadequate fresh air ventilation. To ensure that blower 16 deliversventilation air 18 at a target ventilation flow rate or an equivalentaverage target airflow rate that is appropriate for the size and designof building 10, the flow delivery of blower 16 can be regulated by acontrol system 20. Control system 20 includes an input 22 for manuallyentering a ventilation setting 24, which in turn is communicated to acontroller 26 via a setup signal 28. Ventilation setting 24 and itscorresponding setup signal 28 reflect a specified number of bedrooms anda specified amount of floor space of building 10. The term, “specified”refers to a quantity (e.g., one bedroom, two bedrooms, three bedrooms,1,000 square-feet, 2,000 square-feet, etc.) as determined by thediscretion of one or more individuals (e.g., building owner, tenant,HVAC equipment installer, engineer, inspector, etc.).

In the illustrated example, building 10 has two bedrooms 30 and 32, abathroom 34, a kitchen area 36, and a living room area 38. An exteriorwall 40 of building 10 defines an outdoor area 42 and an indoor area 44(rooms 30, 32, 34, 36 and 38). Building 10 may also include windows 46and doors 48.

In some embodiments, such as the one shown in FIG. 1, blower 12 is partof a primary HVAC system 50, and blower 16 is part of a ventilationsystem 52, wherein the two systems 50 and 52 and their respectiveblowers 12 and 16 can be operated independently of each other. Thisallows the larger, more power-consuming main HVAC blower 12 to bede-energized periodically, while the smaller ventilation blower 16 canrun continuously. This conserves electrical power, as the main HVACblower 12 has a rated maximum flow rate that is several times largerthan that of ventilation blower 16. In other embodiments, however,ventilation system 52 can be a standalone system in a building that doesnot include any type of HVAC system 50.

For illustration, primary system 50 comprises main blower 12, a heatexchanger 54, a network of supply air ducts 56, a network of return airducts 58, and a thermostat 60. Heat exchange 54 may be part of variousknown systems including, but not limited to, an air conditioner,furnace, heat pump, de-humidifier, humidifier, and various adaptationsand combinations thereof. In response to sensing the temperature orhumidity in building 10, thermostat 60 controls the operation of blower12 and heat exchanger 54 to meet the building's temperature or humiditydemand. Blower 12 forces air 14 across heat exchanger 54, which heats,cools, or otherwise conditions the air before supply ducts 56 deliverthe conditioned air to the various rooms of the building. After air 56enters and circulates through the rooms, blower 12 draws the used airback out of the rooms via return air ducts 58. Blower 12 then forces air14 back across heat exchanger 54 for reconditioning.

To provide fresh air, ventilation system 52 comprises ventilation blower16 and control system 20. Control system 20 comprises controller 26,manual input 22, and a drive unit 62 with an electrical output 64 forproviding appropriate electrical power 66 to a motor 68 of blower 16. Itshould be appreciated by those of ordinary skill in the art that one ormore of the motor's various drive components can be integrated withinmotor 68 itself or mounted separately, such as mounted within controlsystem 20.

Although ventilation blower 16 could be installed to discharge air 18into or out of building 10, in this example, blower 16 draws outdoor airthrough a first opening 70 and discharges the air into building 10 via asecond opening 72. This tends to build a slight positive pressure insidebuilding 10. The positive pressure can force the indoor air outside bynatural leakage through windows, doors, or other incidental cracks oropenings in the building. The slightly pressurized indoor air, forexample, may escape the building through a bathroom exhaust vent orthrough a kitchen exhaust hood.

FIGS. 2-5 illustrate other ways of installing blower 16. In FIG. 2, forexample, drive 62 reverses the rotational direction of blower 16 toforce indoor air from second opening 72 to first opening 70, whichcreates a slightly negative pressure inside building 10. The negativepressure can draw fresh outdoor air into the building through adedicated inlet register 73 (with or without a filter 75) or by naturalleakage through windows, doors, or other incidental cracks or openingsin the building.

In FIG. 3, blower 16 is installed to draw fresh outdoor air throughfirst opening 70 and discharge the fresh air through second opening 72to mix with reconditioned supply air in supply duct 56.

In FIG. 4, blower 16 draws fresh outdoor air through first opening 70and discharges the fresh air through second opening 72 to mix withreturn air in return duct 58. Mixing outdoor air within ducts 56 or 58,as shown in FIGS. 3 and 4, can avoid creating an uncomfortable draft atany one location in building 10.

In FIG. 5, blower 16 provides a dual purpose. Blower 16 serves as abathroom exhaust fan as well as an overall building ventilator. Althoughblower 16 could be controlled to provide a generally constant flow ratefor both bathroom ventilation and overall building ventilation,alternatively, blower 16 could be selectively operated in a normal modeand a high-volume mode. In the normal mode, blower 16 could provideoverall building ventilation by exhausting a constant target airflowrate regardless of changes in the indoor/outdoor static pressuredifferential. In the high-volume mode, blower 16 could operate at fullspeed for rapid ventilation of the bathroom. A manual switch, lightsensor, or occupancy senor could be used for selecting the blower's modeof operation.

Regardless of the installation of blower 16, ventilation system 52 needsto ensure that building 10 has adequate ventilation. To do this, system52 should take into account the amount of floor space and the number ofbedrooms in the building, as specified in ASHRAE Standard 62.2-2003.Under certain circumstances, that standard specifies that theventilation flow rate may be specified by the equation,Q=0.01A+7.5(N+1), where “Q” is the target ventilation flow rate in termsof cubic feet per minute, “A” is the specified amount of floor space inunits of square-feet, and “N” is the specified number of rooms (e.g.,one, two, three rooms, etc.). An approximation of that relationship canbe tabulated as shown in table 74 of FIG. 6. It should be noted that theabove-specified equation and corresponding tabulation is not the onlypossible acceptable relationship between a target ventilation flow rateand a building's parameters, and that additional relationships specifiedby ASHRAE or other predetermined relationships are well within the scopeof the invention.

To avoid a technician having to manually calculate a building'sventilation requirements, adjust and calibrate the ventilation blower,and manually test the results, ventilation system 52 does thisautomatically by providing controller 26 with manual input 22. Manualinput 22 enables a user to enter one or more parameters that reflect thebuilding's amount of floor space and number of bedrooms. The parameteror parameters are represented by setup signal 28, which input 22communicates to controller 26. Based on setup signal 28, controller 26provides a command signal 76 that directs drive unit 62 to deliverappropriate electrical power 66 for blower 16 to provide the desiredtarget ventilation flow rate.

Control system 20 preferably (but not necessarily) regulates theventilation flow rate at the target ventilation flow rate. This can bedone in various ways including, but not limited to, regulating orvarying the rotational speed of blower 16, adjusting a damper associatedwith blower 16, or cycling blower 16 on and off at a duty cycle thatprovides an average target ventilation flow rate over a predeterminedperiod.

In a currently preferred embodiment of the invention, motor 68 of blower16 is a variable speed motor that drives a fan wheel 16′ of blower 16.Fan wheel 16′ is schematically illustrated to represent any type ofair-moving element including, but not limited to, a centrifugal blower,axial fan, etc. Depending on the type of variable speed motor, driveunit 62 may be an inverter, DC voltage regulator, electronicallycommutated motor drive, or some other appropriate conventional drivecircuit that can respond to speed command signal 76 from controller 26.Controller 26 is schematically illustrated to represent any commoncontrol circuit that can provide an appropriate speed command signal inresponse to an input, such as setup signal 28.

To create setup signal 28, manual input 22 may assume a variety offorms, thus manual input 22 is schematically illustrated to representany type of human interface between a user and a controller. Examples ofmanual input 22 include, but are not limited to, one or more electricalswitches (e.g., dipswitches), electrical jumpers, PDA, laptop, computer,remote control (e.g., radio, infrared, etc.), Internet communication, adial (potentiometer, rotatable selector switch, etc.), and a touchpad(e.g., keyboard, pushbuttons, touchscreen, etc.).

In FIG. 7, for instance, manual input 22 a is a plurality of dipswitchesfor entering ventilation settings that setup signal 28 conveys frominput 22 a to controller 26. One set of switches 78 can be used forentering the amount of floor space, and another set of switches 80 canbe for entering the number of rooms.

In FIG. 8, manual input 22 b includes a selector switch or a dial 98that is used in conjunction with a reference chart 82. A user refers tochart 82 for determining a ventilation setting that correctly representsthe building's floor space and number of bedrooms. If building 10, forexample, has 2,000-ft² and three bedrooms, chart 82 indicates that dial98 should be set to the ventilation setting labeled “C,” which in turnresults in setup signal 28 being at a value that is appropriate for sucha building. With the use of chart 82, only one dial 98 (or equivalentinput device) is needed to represent both the floor space and number ofbedrooms.

In FIG. 9, manual input 22 c includes a touchpad 100 with up and downarrows 84 and 86 for making a selection 88 from A-J of chart 82. In thisexample, the letter “D” is chosen instead of “C.” According to chart 82,selecting “D” would be an appropriate ventilation setting for a3,000-ft² building with four bedrooms.

Based on setup signal 28 (which in turn is based on a user-selected,manually-entered ventilation setting) controller 26 provides commandsignal 76 at a value that tells drive unit 62 to run blower 16 at thetarget ventilation flow rate. The actual flow rate, however, may tend tovary due to a variety of factors including but not limited to changes inthe static pressure differential between the indoor and outdoor air. Toensure that blower 16 is actually delivering the target flow rateregardless of moderate changes (normal anticipated changes of less thana 0.3 inch column of water) in the static pressure differential betweenthe outdoor area and the indoor area, in some embodiments, controlsystem 20 regulates the blower's rotational speed to account for suchchanges. This can be accomplished in different ways.

In some cases, the actual flow rate through blower 16 can be determined,estimated or perceived as being a function of the blower's rotationalspeed and the power consumption of motor 68. Such a relationship isreadily determined by knowing the operating characteristics of fan wheel16′. The motor's rotational speed can be measured directly or it can becalculated based on a known relationship between the motor's speed and,depending on the type of motor, the frequency or voltage of electricalpower 66. The motor's power consumption can be calculated based on thevoltage and current supplied to motor 68.

Since control system 20 or drive unit 62 may “know” the voltage, currentand frequency of electrical power 66, system 20 may be able to regulatethe output of blower 16 without additional externally generatedfeedback. In some cases, however, controller 26 may be provided withfeedback, such as a flow rate signal 90. Flow rate signal 90 may comefrom drive unit 62; flow, speed, or pressure sensors associated withblower 16; a current sensor associated with electrical power 66; and/orother conventional sources. Flow rate signal 90 can be generatedinternally within controller 26, generated internally within drive 62,or generated externally relative to control system 20. In FIG. 2, forinstance, flow rate signal 90′ is created externally from a differentialpressure sensor 92 that senses the static pressure upstream anddownstream of blower 16.

To ensure adequate ventilation even when HVAC system 50 is inactive dueto mild outdoor temperatures, ventilation system 52 can be controlled tooperate substantially independently of primary HVAC system 50. FIGS. 1,2, 4 and 5 show examples of HVAC system 50 and ventilation system 52being controlled independently, and FIG. 3 schematically shows anelectrical connection 94 that couples controller 26 to thermostat 60.With the system of FIG. 3, thermostat 60 and controller 26 can beintegrated into a single control unit and can be housed within a commonenclosure 96.

Referring back to FIG. 7, in some cases, the control system may alsoinclude an input 81 for selectively operating in one or more alternatemodes other than or in addition to a normal mode 83 where the building'ssize, floor space or number of rooms is considered. In an alternate modeof operation, blower 16 may deliver an alternate airflow rate that isgreater or less than the normal target airflow rate and may even be at aflow rate of zero (i.e., substantially no flow). Examples of alternatemodes include, but are not limited to, an economizer mode 85, anoccupancy mode 87, a vacation mode 89, etc.

In the economizer mode, blower 16 delivers ventilation air at a highervolume than what is required for normally acceptable ventilation. Theadditional outside air could provide “free cooling” when the outside airis reasonably dry and cooler than the indoor air.

In the occupancy mode, control system 20 may deactivate blower 16 uponsensing that the building is unoccupied or that the building's occupancyis below a certain occupancy level. A motion or light sensor, forexample, could provide control system 20 with an indication of thebuilding's occupancy.

In the vacation or override mode, a user may deactivate blower 16 tosave energy when the user knows that the building will be unoccupied foran extended period.

In some cases, control system 20 may include an audio or visual alarmsignal 91 that becomes automatically triggered upon blower 16 failing toprovide the target ventilation flow rate. Signal 91, for example, mayturn on when blower 16 is running at a maximum or a predetermined highspeed yet is still unable to provide the target ventilation flow rate.

Although the invention is described with reference to a preferredembodiment, it should be appreciated by those of ordinary skill in theart that other variations are well within the scope of the invention. Itis conceivable, for instance, that blower 16 could not only be cycled onand off at a duty cycle that provides an average target ventilationrate, but the blower's rotation could be reversed at each cycle to helpmaintain a more neutral or predetermined pressure in building 10.Moreover, the equation or relationship between the required targetventilation rate and the building's parameters may be adjusted due tolocal climate, regulating the ventilation flow rate by cycling theventilation blower on and off, or various other reasons. Therefore, thescope of the invention is to be determined by reference to the followingclaims:

What is claimed is:
 1. An HVAC system for a building that defines anoutdoor area and an indoor area, the building includes a specifiednumber of rooms and a specified amount of floor space, the HVAC systemcomprising: a main blower configured to deliver temperature-conditionedair into the indoor area through a first supply path that extends fromthe main blower to the indoor area; a ventilation blower configured todeliver air from the indoor area and into the outdoor area through asecond supply path that extends from the ventilation blower to theoutdoor area; wherein the second supply path is independent from a firstreturn path that extends from the indoor area to the main blower; acontroller operatively coupled to the ventilation blower to render theventilation blower selectively operable in a normal mode and analternate mode, such that the controller determines the actualventilation flow rate through the ventilation blower as a function ofthe rotational speed of the ventilation blower and the power consumptionof the motor of the ventilation blower; and a control system having anelectrical output and a manual input, wherein the electrical output isoperatively coupled to the ventilation blower for urging the ventilationblower to move the ventilation air at a target ventilation flow rate,wherein the target ventilation flow rate is based on a setup signal thatis communicated to the controller via the manual input, wherein thesetup signal is based on the specified number of rooms and the specifiedamount of floor space.
 2. The HVAC system of claim 1, wherein the manualinput includes at least one of a touchpad, an electrical switch, and adial.
 3. The HVAC system of claim 1, wherein the ventilation blower issmaller than the main blower.
 4. The HVAC system of claim 1, wherein thecontrol system regulates a rotational speed of the ventilation blower.5. The HVAC system of claim 1, wherein the control system cycles theventilation blower on and off to achieve the target ventilation flowrate as averaged over a predetermined period.
 6. The HVAC system ofclaim 1, wherein the ventilation blower operates substantiallyindependently of the main blower.
 7. The HVAC system of claim 1, whereinthe control system is configured to determine the actual ventilationflow rate through the ventilation blower as a function of the rotationalspeed of the ventilation blower and the power consumption of the motor.8. The HVAC system of claim 1, wherein the control system is configuredto selectively regulate a rotational speed of the ventilation blowerover a range of rotational speed values, the range including arotational speed value of zero and a plurality of positive rotationalspeed values, in response to a change in the determined actual flowrate.
 9. An HVAC system for a building that defines an outdoor area andan indoor area, the building includes a specified number of rooms and aspecified amount of floor space, the HVAC system comprising: a mainblower configured to deliver temperature-conditioned air into the indoorarea through a first supply path that extends from the main blower tothe indoor area; a ventilation blower configured to deliver air from theindoor area and into the outdoor area through a second supply path thatextends from the ventilation blower to the outdoor area; wherein thesecond supply path is independent from a first return path that extendsfrom the indoor area to the main blower; and a controller operativelycoupled to the ventilation blower to render the ventilation blowerselectively operable in a normal mode and an alternate mode, such thatthe controller determines the actual ventilation flow rate through theventilation blower as a function of the rotational speed of theventilation blower and the power consumption of the motor of theventilation blower; wherein the controller provides an average targetventilation flow rate through the ventilation blower as averaged over apredetermined period by cycling the ventilation blower on and off toachieve an average target ventilation flow rate through the ventilationblower as averaged over a predetermined period.
 10. The HVAC system ofclaim 9, wherein the target ventilation flow rate is based on thespecified number of rooms and the specified amount of floor space. 11.The HVAC system of claim 9, wherein the target ventilation flow rate isbased on a certain occupancy level of the building.
 12. The HVAC systemof claim 9, wherein the control system regulates a rotational speed ofthe ventilation blower to maintain the average target airflow rate. 13.The HVAC system of claim 9, wherein the control system selectivelyoperates the ventilation blower at a normal mode and an alternate modesuch that the average target airflow rate occurs during the normal mode,and an alternate airflow rate occurs during the alternate mode, whereinthe alternate airflow rate is distinguishable from the average targetairflow rate.
 14. The HVAC system of claim 13, wherein the alternateairflow rate is greater than the average target airflow rate.
 15. TheHVAC system of claim 13, wherein the alternate airflow rate is less thanthe average target airflow rate.
 16. The HVAC system of claim 13,wherein the alternate airflow rate is substantially equal to zero. 17.The HVAC system of claim 9, wherein the controller includes an input forreceiving a setup signal that is based on at least one of the specifiednumber of rooms and the specified amount of floor space.
 18. The HVACsystem of claim 9, further comprising: an alarm signal for indicatingwhen the ventilation blower may be failing to achieve the targetventilation flow rate.
 19. The HVAC system of claim 18, wherein thealarm signal is triggered by a rotational speed of the ventilationblower reaching a certain limit.
 20. An HVAC system for a building thatdefines an outdoor area and an indoor area, the HVAC system comprising:a main blower configured to deliver temperature-conditioned air into theindoor area through a first supply path that extends from the mainblower to the indoor area; a ventilation blower configured to deliverair from the indoor area and into the outdoor area through a secondsupply path that extends from the ventilation blower to the outdoorarea; wherein the second supply path is independent from a first returnpath that extends from the indoor area to the main blower; and acontroller comprising a drive unit for providing power to a motor of theventilation blower, the controller operatively coupled to theventilation blower to render the ventilation blower selectively operablein a normal mode and an alternate mode, such that: the controllerdetermines the actual ventilation flow rate through the ventilationblower as a function of the rotational speed of the ventilation blowerand the power consumption of the motor of the ventilation blower;wherein in the normal mode, the ventilation blower delivers air at anaverage target airflow rate that is substantially constant regardless ofa moderate change in a static pressure differential between the outdoorarea and the indoor area, and wherein in the alternate mode, theventilation blower moves delivers air at a high-volume airflow rate thatis greater than the average target airflow rate, wherein the high-volumeairflow rate and may change in response to the moderate change in thestatic pressure differential between the outdoor area and the indoorarea.